1. Field of the Invention
The present invention relates to heat exchangers, and more specifically, to heat exchangers in which a plurality of heat transfer tubes are inserted into tube insertion holes formed through each of a pair of tanks. Such heat exchangers are suitable for use in an air conditioning system for vehicles.
2. Description of Related Art
Heat exchangers having a pair of tanks and a plurality of flat, heat transfer tubes interconnecting the tanks are known. Such heat exchangers may be manufactured by temporarily assembling respective parts and brazing together the assembled parts in a furnace at the same time. In the manufacture of such heat exchangers, for example, as depicted in FIG. 14, end portions of flat, heat transfer tubes 103 are inserted into respective tube insertion holes 102 formed through a seat plate 101 of a tank 100. Fins 104 are interposed between adjacent heat transfer tubes 103.
In such heat exchangers, however, a variety of insertion lengths of respective heat transfer tubes 103 into tank 100 may occur. If the insertion length of heat transfer tube 103 is too long (for example, as in portions P1), flow resistance in tank 100 may increase. On the other hand, if the insertion length of heat transfer tube 103 is too short (for example, as in portions P2), the area for brazing between the outer surface of heat transfer tube 103 and the inner surface of tube insertion hole 102 may decrease, thereby reducing the strength of the bond. Further, although heat transfer tubes 103 and fins 104 are held by a jig (not shown) from both sides in their stacked direction when the assembled parts are brazed together in a furnace, because of a difference in the coefficient of thermal expansion between the steel jig and the parts of the heat exchanger constructed from an aluminum material or the like, the heat exchanger may be crimped strongly by the jig, and the end portions of heat transfer tubes 103 may be deformed.
In response to this problem, a structure, as depicted in FIGS. 15-17, is proposed in Japanese Patent Application Publication No. JP-A-2-242095, wherein portions 106 protruding outwardly from heat transfer tube 105 and extending across the width or in a radial direction of heat transfer tube 105 are formed on both end portions of heat transfer tube 105. By this configuration, the tube insertion lengths of the respective tubes 105 are made more uniform, and a positional shift between the tubes and the tanks is prevented.
In such heat exchangers, however, if heat transfer tube 105 is inserted forcibly, tube insertion hole 102 of seat plate 101 may be deformed, and the inner surface of the deformed tube insertion hole 102 overlap protruded portion 106. Consequently, the tube insertion length may not be regulated. Further, at that time, if a large force operates from the inner surface side of tube insertion hole 102 against protruded portion 106, tube 105 may be deformed. If the heat transfer tube 105 is deformed, a decrease in brazing strength or an increase in flow resistance, or both, may occur.